.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" Copyright (c) 2020      Google, LLC. All rights reserved.
.\" $COPYRIGHT$
.TH MPI_Group_size 3 "#OMPI_DATE#" "#PACKAGE_VERSION#" "#PACKAGE_NAME#"
.SH NAME
\fBMPI_Group_size\fP \- Returns the size of a group.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Group_size(MPI_Group \fIgroup\fP, int \fI*size\fP)

.fi
.SH Fortran Syntax
.nf
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_GROUP_SIZE(\fIGROUP, SIZE, IERROR\fP)
	INTEGER	\fIGROUP, SIZE, IERROR\fP

.fi
.SH Fortran 2008 Syntax
.nf
USE mpi_f08
MPI_Group_size(\fIgroup\fP, \fIsize\fP, \fIierror\fP)
	TYPE(MPI_Group), INTENT(IN) :: \fIgroup\fP
	INTEGER, INTENT(OUT) :: \fIsize\fP
	INTEGER, OPTIONAL, INTENT(OUT) :: \fIierror\fP

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
group
Group (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
size
Number of processes in the group (integer).
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
MPI_Group_size returns in \fIsize\fP the number of processes in the group. Thus, if group = MPI_GROUP_EMPTY, then the call will return size = 0. On the other hand, a call with group = MPI_GROUP_NULL is erroneous.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument.
.sp
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

